Now the chemical bactericides are often used to sterilize the SRB (sulfate reducing bacteria) in the treatment process of oilfield produced-water, but this method always accompany with disadvantage, such as lower efficiency, environment pollution, high cost, drug-fast of bacteria, and the side-effect of reaction with the other agent adding in water treatment. We Daqing oilfield should dispose about 500 million tons produced water, a great effort should do to get a bactericide method both of high efficiency and low cost to dispose such a mass of produced-water.

This paper show you that how we use ultraviolet radiation method to sterilize the SRB? and what good effect we did get?

First, the Oily produced-water being treatment can become very clear, its light transmissivity is 60-80%, this is clear enough to let the ultraviolet ray to penetrate through. One of this sort equipment can dispose 10 thousand cubic metrers produced-water. After being sterilized, the number of SRB declines from 100-1000 per ml. to less than 10 per ml. , but the chemical bactericide just down the number of SRB to 100 per ml. At the same time, it can sterilize the metatrophic bacteria _TGB_ and iron bacteria _FB_ as well, which can be reduced both the two bacteria from 10-100 thousands per ml. to 100 per ml. and this method just cost of one fifth of chemical bactericide method.

Introduction

Daqing Oilfield usually re-inject produced-water which is deeply disposed in oil development. Sulfate reducing bacteria (SRB) in kind of re-injected water causes corrosion and dirt depositing on injecting facilities and pipelines, and damages the formation as well. At present, the common practice of disinfection in China is adding disinfectant in produced-water. Both the insufficient quantity of disinfectant agent used because of its expensive price and no periodical cleaning of injecting pipeline adversely affect the disinfecting effect. Metabolite of SRB, mingled with emulsified oil and secretions of TGB and FB on the pipe wall, form a biological membrane dirt which covers the pipe wall, where provides an environment of lack of oxygen. At the same time, under the biological membrane dirt, there is low chemical concentration which causes drug-fast SRBs, which reproduce greatly on the pipe-wall. Chemicals are added with intermittent way for every 4 or 5 days once. This, however, always causes the increasing quantity of bacteria for lower concentration of disinfectant between the two times adding disinfectant, and the quality of re-injected water is not satisfied for unstable and low content of bacteria.

In order to improve the qualification rate of re-injected water, especially of sulfate reducing bacteria, both a com-pound disinfectant with low cost and long-term of bacteria depressing and a new better disinfection method are required. Ultraviolet rayed disinfection facilities, which have been successfully developed, shows a great potential in re-injecting the produced water on oilfield, is adopted and present a good result in Z-11 oil gathering station in Daqing Oilfield.

1_Principles of ultraviolet rayed disinfection and the result in lab.

1) Principles

Generally, ultraviolet rays is usually divided into three different wavebands: band A (wavelength of 315-400nm), B(280-315nm) and C(200-280 nm). Among them, the wave band C has the best sterilizing effect.

When bacteria are radiated by a certain dosage of ultraviolet ray, their internal structures of deoxyribonucleic acid (DNA) are destroyed, so does their reproductive capacity of bacteria. Therefore, bacteria are destroyed without using any chemicals. Ultraviolet ray restrains and disinfects all bacteria; the only key problems are the dosage used according to the specific bacteria properties.

2) Laboratory experiment

All kinds of produced-water are tested with ultraviolet ray C fluorescent tube disinfecting method. The following table_Table 1_shows data about SRB, TGB and FB content measured at different flow rate.

The result indicates that an average content of SRB is 0.2/ml, and an average disinfecting rate is 99.9%, TGB and FB content is 6/ml and 12/ml respectively, with an average disinfecting rate of 99.9%.

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